The document provides a comprehensive overview of human cognitive mechanisms from neural activity to subjective experience. It discusses how physical interactions in the brain give rise to phenomenal experiences like vision. The key points covered include: 1) The basic mechanisms of action potentials, synaptic transmission, neuroplasticity, and neuromodulation that underlie information processing in the brain. 2) How sensory inputs are processed through automatic and controlled mechanisms to perform actions, forming an action-perception cycle. 3) The role of memory, sensations, and mental processes in perception, with different memory theories and the neural basis of memory systems. 4) How information is retained and recalled through neural activity patterns preserved by long-term

1. A comprehensive outline of
human cognitive mechanism
From neural activity to vision: how physical becomes phenomenal

2. Introduction
• Current understanding of cognition involves knowledge of individual
processes like neuronal activity, memory and behavior
• Each of these processes are known in great details
• Still, it cannot be explained why the activities in the neurons becomes a
subjective experience like visualization of the world
• In other words, the phenomenal experience cannot be reduced to physical
interactions in the brain
• The purpose of this work is to bring all the processes involved in cognition
together and relate them with each other so that a complete chain of
events is established from physical interactions to phenomenal experience

3. What does the brain do?
• Brain performs various intelligent activities like reasoning and judging
• The ultimate purpose of all these activities is to perform movement
• In other words, brain is a movement processor
• Through autonomic nervous system it optimizes the functioning of different
systems of the body to make the body perform those movements as a single unit
• It does not have an external programmer to program it beforehand
• Its self-programming capacity has developed through evolution
• Brain contains a network of neurons which gets inputs from the receptors in one
hand and sends output to different organs like muscles and glands
• It develops and remembers the required knowledge and skills and use them to
execute appropriate actions
• Actions are essential for survival

4. The basic mechanisms: Action potential
• The resting potential of a neuron is
about –70 mv
• Passage of positive and negative ions
through various ion channels in the cell
membrane maintains this potential
• Synaptic activities causes enhanced
movement of ions and change the
membrane potential
• If a neuron depolarizes to -55mv action
potential is generated in the neuron
• The action potential travels through the
axon and reaches the synapses leading
to release of neurotransmitter
Blaustein, M., Kao, J., & Matteson, D. Cellular Physiology and Neurophysiology: Mosby Physiology Series Ch. 12 & 13 (Elsevier, St. Louis, Missouri, 2020).

5. The basic mechanisms: synaptic transmission
• The action potential travels through the axon and reaches the synapses leading to
release of neurotransmitter
• The neurotransmitter reaches the post-synaptic neuron and changes the resting
membrane potential (post synaptic potential)
• Excitatory post synaptic potential (EPSP) depolarizes the post-synaptic neuron
• Inhibitory post synaptic potential (IPSP) hyperpolarizes the post-synaptic neuron
• If aggregation of EPSPs and IPSPs depolarizes the membrane potential to -55 mv
Action potential is generated
• The action potential travels through the axon to the synapses and release the
neurotransmitter to next set of neurons
• Some synapses release modulatory neurotransmitter which acts via second
messenger and bring metabolic changes in the postsynaptic neuron
(neuromodulation)
Blaustein, M., Kao, J., & Matteson, D. Cellular Physiology and Neurophysiology: Mosby Physiology Series Ch. 12 & 13 (Elsevier, St. Louis, Missouri, 2020).

6. The basic mechanisms: neuroplasticity
• He neuron network does not remain the same after a neural activity
• The change in the network as a result of neural activity is called neuroplasticity, which
can be of two types
• Structural neuroplasticity
• Frequent activity increases the number of connections between the neurons and lack of activity
cause disappearance of the connection between the neurons
• Bailey, C. H., & Chen, M. (1988). Long-term memory in Aplysia modulates the total number of varicosities of
single identified sensory neurons. Proceedings of the National Academy of Sciences, 85(7), 2373-2377.
• Synaptic neuroplasticity
• Long term potentiation (LTP)
• When two neurons fire at the same time their connecting synapses are potentiated
• The synaptic activity cause greater degree of depolarization in the post-synaptic neuron
• Long term depression (LTD)
• When two neurons fire at different times like the post-synaptic neuron fires before thew pre-synaptic neuron,
their connecting synapses are depressed
• The synaptic activity causes lesser degree of depolarization in the post-synaptic neuron
Blaustein, M., Kao, J., & Matteson, D. Cellular Physiology and Neurophysiology: Mosby Physiology Series Ch. 12 & 13 (Elsevier, St. Louis, Missouri, 2020).

7. The basic mechanisms: Neuromodulation
• Metabotropic receptors
• Some neurotransmitters alters the metabolic activity of the neurons causing alteration of
excitability of the neurons and the synapses
• These act on the receptors which release a second messenger like cAMP
• Reticular activating system
• The reticular formation determines which neurons will be available for processing of information
• The state of arousal depends on the available neurons
• In this way reticular formation controls the level of consciousness
• The limbic system
• It tunes the excitability of available neurons and synapses
• This creates a hierarchy among the neurons
• Neurons up in hierarchy are excited first and control the excitation of neurons lower in hierarchy
• By altering the hierarchy limbic system controls the emotional and behavioural response to a
situation

8. Outline of information processing in brain
Action-perception cycle
• Basic Mechanism
• Generation of Action potential
• Synaptic transmission
• Input
• External senses
• Vision, hearing, smell, taste and touch
• Internal senses
• Vestibular, proprioceptive and visceral
• Output
• Autonomic
• Voluntary
• Attention dependent – automatic processing
• Attention independent – controlled processing
Intelligent processes
• Attention
• Dorsal network – goal pursuit
• Ventral network – alert system
• Subcortical nuclei – sensory input control
• Mental activities
• Memory formation – library of neuron memory
• Memory activation – perceptual experience, conceptual
thoughts and feeling of emotions
• Memory consolidation – optimisation of library
• Memorization
• Neuroplasticity
• Structural
• Functional
• Neuromodulations
• Arousal – Reticular activating system
• Emotions and behaviours – Limbic system

9. Neural basis of
information processing
• Each neuron has a memory
• When excited the memory is
expressed as its function
• The function of a neuron is specific
• Processing logically activates
specific neurons so that actions are
performed based on receptor
inputs
• The result of the actions are again
detected by the receptors setting
up an action-perception cycle

10. The basic mechanisms: Automatic and
controlled processing
• Automatic processing occurs with out attention
• Example is walking through a familiar road
• Controlled processing involves attention
• Example – performing a new motor activity like learning to ride a bicycle
Posner, M. I., Snyder, C. R., & Solso, R. (2004). Attention and cognitive control. Cognitive psychology: Key
readings, 205, 55-85.
Shiffrin, R. M., & Schneider, W. (1977). Controlled and automatic human information processing: II. Perceptual
learning, automatic attending and a general theory. Psychological review, 84(2), 127.

11. The basic mechanism: Automatic processing
• When a person walks down a familiar road, hardly any attention becomes necessary
• Brain automatically sends action potentials to various muscles based on receptor input
• The result of the movement is sensed again leading to further actions
• In this way an action-perception cycle is established and the body functions in an automatic mode without any need of explicit
attention
• This is called automatic processing
• Due to neuroplasticity, the connections and synapses are adjusted based on past activities
• The synapses then guide the action potential through the most probable paths to the muscles
• Neuromodulators tunes the responsiveness of the neurons and synapses altering the hierarchy of the paths
• The senses feed the network with new patterns of activities
• With ongoing activities, the appropriate neurons get depolarized
• More depolarization makes a neuron more primed for excitation
• Action potential travels through the most primed neurons which succeed to reach the threshold level of depolarization
• As a result, actions continue based on the receptor input without any attention
• Neuroplasticity ensures action potential travels through paths learned from past experience

12. Libet experiments: automatic processing
underlies controlled processing
• Starting from Libet experiments on free
will, studies have suggested that neural
activities (readiness potential) precede the
actual self-awareness of initiation of an
action
• Libet experiments show that, the
processes which appear to be controlled
by some voluntary mechanism are also
the results of automatic processing
• Libet, B., Gleason, C. A., Wright, E. W., &
Pearl, D. K. (1993). Time of conscious
intention to act in relation to onset of
cerebral activity (readiness-potential). In
Neurophysiology of consciousness (pp.
249-268). Birkhäuser, Boston, MA.

13. Memory, Sensations and the Mind
• Though automatic processing occurs without attention, it does not occur silently
• In a silent mechanism, it may be difficult to carry out functions like thinking and communication, because the activities will not be
distinctly identifiable
• Sensations are generated when the neurons are stimulated
• When active, a neuron can generate a specific sensation
• To create a specific sensation, the precursor of that sensation must be present in a neuron at the time of activation
• The precursor present in a neuron is the memory of that neuron
• All the memory units present in the neurons form a library
• As the activity passes through the network, neurons in the path are stimulated and a selection of memory from the library are
activated into sensations
• These sensations constitute different mental activities
• In other words, all the active sensations together constitute the mind
• Sensations act as tags making the neural activities identifiable
• When sensations are there, It becomes possible to think and communicate by working on those feelings
• All subjective feelings like "I am seeing' or 'doing' are just superadded sensations, which arise about 350 ms after start of
underlying automatic processing (Libet experiments)

14. Sensations and Perception
• Movement is essential for survival
• For effective movement environmental awareness is required
• The only source of information about environment is the inputs coming from the sensory
receptors
• Perception is the act which process the inputs coming from the senses to create
awareness of the environment
• Processing results in execution of required actions through logical activation of a series of
neurons
• The logic of activation depends on two factors
• Neuroplasticity involving the connections and synapses resulting from the past activities
• Neuromodulation which adjusts the availability (arousal by reticular activating system) and
hierarchy of the neurons (Limbic system), in real time
• Activation of a series of neuron results in generation of a series of sensations
• The object of perception is represented by those sensations

15. An important observation
• It has been observed that the neurons which are activated during and experience
are again activated during recall of that experience
• Why?
• Nyberg, L., Habib, R., McIntosh, A. R., & Tulving, E. (2000). Reactivation of
encoding-related brain activity during memory retrieval. Proceedings of the
National Academy of Sciences, 97(20), 11120-11124.
• Wheeler, M. E., Petersen, S. E., & Buckner, R. L. (2000). Memory's echo: vivid
remembering reactivates sensory-specific cortex. Proceedings of the National
Academy of Sciences, 97(20), 11125-11129

16. Memory: Atkinson and Shiffrin Model (1968)
• Atkinson, R. C., & Shiffrin, R. M. (1968). Human memory: A proposed system
and its control processes. In Psychology of learning and motivation (Vol. 2, pp.
89-195). Academic Press, New York.
Sensory
memory
Short-term
memory
Long-term
memory
Input
Unattended
information
is lost
Unrehearsed
information
is lost
Some
information
is lost over
time
Rehearsal
Encoding
Retrieval
Attention

17. Memory: Baddley Hitch Working Memory
Model (1974)
• Baddeley, A. (1974). Hitch GJ. Working memory. The psychology of learning
and motivation: advances in research and theory. (Vol. 8, pp. 47-89 Academic
Press, New York, 1974).
Episodic buffer
Central
Executive
Phonological
loop
Visuospatial
Sketchpad
Visual
semantics
Episodic
LTM
Language

18. Memory: Other theories
• According to Cowan’s theory (1988), working memory is a form of
activated long term memory
• Levels of Processing(Craik & Lockhart, 1972)
• the strength of a memory trace depends upon the quality of
processing, or rehearsal, of a stimulus
• Cowan, N. (1988). Evolving conceptions of memory storage, selective attention, and their mutual
constraints within the human information-processing system. Psychological bulletin, 104(2), 163-
191.
• Craik, F. I., & Lockhart, R. S. (1972). Levels of processing: A framework for memory research.
Journal of verbal learning and verbal behavior, 11(6), 671-684.

19. What is memory?
• The term memory can be used in two ways
• Memory of a neuron
• It is the precursor of the sensation a neuron produces when active
• It is a pre-fabricated element with respect to the time of activation
• It is again reconsolidated after production of a sensation
• Evidence suggest that protein synthesis blockers affect the reconsolidation process
• Gold, P. E. (2008). Protein synthesis inhibition and memory: formation vs amnesia. Neurobiology of learning and memory, 89(3), 201-211
• Personal Memory of an individual
• Memory of the neurons is the essential ingredient of personal memory
• They are like the prefabricated building blocks of personal memory
• Activation of neural memory into sensations give rise to both real-time experience as well as personal memory
• The pattern and sequence of sensations depend upon the neural activity
• Medial temporal lobe and hippocampus play an important role in encoding and retrieval of the pattern and sequence of activation of neurons
• As a result, the network remembers the pattern & sequence of past activities and recreate them later to think and remember
• Real time experience and recollection of an experience use the same library of neuron memory
• Immature development of memory library lead to reduced cognitive ability (example amblyopia involving visual cognition)
• Loss of neuron memory leads to dementia
• Dysfunctions of these encoding and retrieval activities lead to amnesia

20. Neural basis of memory
and mental processes
• Sensations arise as a result of neural
stimulation
• The characteristics of a sensation is
determined by the memory of that neuron
• Memory units from all the neurons form a
common library
• Characteristics of a phenomenal experience
depends upon the pattern of neural activities
which in turn determines the order of
generation of the sensations
• Pattern of neural activity depends upon the
network architecture, synaptic plasticity and
modulation of excitability of the neurons
• Different types of memory phenomenon
results from different activity patterns in the
network

21. Neural basis of memory
and mental processes
• Long term memory: library of memory units in neurons
• Implicit memory: memory activation through automatic
processing
• Explicit memory: memory activation through controlled
processing
• Sensory memory: memory units activated at a particular time
through automatic processing
• Working memory: memory units activated at a particular time
through controlled processing
• Short term memory: sensory memory accessed into working
memory through attention
• Episodic memory: Long term memory accessed into working
memory through hippocampal contextual priming
• Semantic memory: Long term memory accessed into working
memory through hippocampus independent direct cortical
priming

22. Retention and recall of information in the
network
• Information from the receptors is processed to execute actions
• The processing generates sensations which results in both real time experience and recollection
of an experience
• Presence of an optimized library of neural memory is a prerequisite for information processing
• With out the memory present in the neurons no perception is possible
• To memorize an experience no new neural memory unit is needed
• Neither the existing memory units are copied from one store to another
• LPTs and LTDs formed during the experience preserve the activity pattern of an experience
• To remember the experience the same neurons are excited in the same sequence using the saved
footprints (LPTs and LTDs )
• The library of neural memory units forms the basis of long-term memory
• As they can be arranged in almost infinite number of ways to generate the required experience,
long-term memory capacity appears to be limitless

23. Automatic processing and sensory memory
• When sensory information is processed, it is held in the memory for a short
period of time
• During this short period, if the information draws attention, then it stays in
the memory for longer duration
• Otherwise, it is lost after a short duration
• This momentary storage of information is known as sensory memory
• This shows that automatic processing does not occur silently
• When a neuron becomes active, it generates a sensation
• The sensation is extinguished when the activity stops
• This brief duration of neural activity and persistence of sensation is the
reason behind the sensory memory

24. Controlled processing
• Automatic processing is fast and energy efficient
• It is mostly a bottom-up processing, starting from the receptors and moving towards the organs of action
• Most of the actions are performed through this process
• In every situation, there remain some novel element in every situation which needs real time processing of a
unique response
• As automatic processing is pre-programmed, it cannot process a novel response which is not in its memory
• So, there must be another mechanism to firstly modify the automatic process in real time and secondly
program it for future
• This is done through controlled processing, with following characteristics
• Intelligent process
• Top-down processing where the activity starts at attention control centers
• It modifies the automatic response in real time to meet the demand of novelty arising from the uniqueness of a situation
• It brings short- and long-term changes in the network to keep it optimized to face the changing demands of the environment
• The cortical and subcortical areas responsible for top-down processing, constitute the attention network

25. Attention network
• Components
• Dorsal network is responsible for goal pursuit
• Ventral network remains as guard and becomes active if there is any unexpected sensation
• Subcortical nuclei control the sensory input
• Attention is also an automatic process, but it gets programmed to control the activity of other areas of the brain using internal logic of the
network
• Attention mechanism can be compared to the driving of a car
• Automatic processing is like the internal mechanism which makes the care move
• The subcortical nuclei are like the steering wheel which controls the sensory input which will be processed
• This feeds the automatic processing with matter to be processed
• The dorsal network is like the driver who guides the automatic processes which way to go
• The ventral network is like the side passenger who alerts the driver if there is a roadblock ahead and a diversion is required

26. Automatic vs. controlled processing
• In automatic processing arrival of information depends on changes in external environment
• So, sensations last for a short while because newer sensations replace older sensations
• As the neuron goes back to the resting state after passage of action potential, the sensation disappears
• As the activity passes through already reinforced synapses there is minimal new long-term changes
• So, the sensation patterns are not remembered, and no memory of the experience ls retained beyond a very
short period of time (sensory memory)
• Attention controlled processing on the other hand, is driven by internal conditioning of the network
• So, the sensations can be sustained longer by controlling the sensory input and selectively letting certain
activities to continue
• This results in short-term memory
• Controlled processing leads to more elaborate processing of information and retention of that activity
through neuroplasticity
• Because of new footprints, the attention driven activities are not immediately forgotten
• This results in awareness of the sensation, which can be thought about, memorized and remembered for
longer duration

27. Attention and Consciousness
• A study of the organization of neural network makes it clear that there is no separate or
specialized consciousness center inside or outside the brain which becomes conscious about all
the sensation those are arising as a result of neural stimulation
• Each sensation is a conscious feeling in itself
• So, collection of all the sensation are automatically becomes a conscious experience
• The thought, ‘I am experiencing’ is a collection of sensations
• What is though as consciousness is actually the awareness of sensations
• A sensation though consciously felt, is momentary
• Awareness occurs when the information is stored as short- and long-term memory
• Attention mechanism is responsible for sustaining a momentary sensation as short-term memory
• The resulting synaptic modifications lead to longer term storage of information
• Attention driven activities use the synaptic footprints of past activities to generate additional
sensations giving rise to thoughts

28. Attention and intelligence
• Automatic processing is programmed by intelligent processing but does not use intelligence in
real-time
• Attention network on the other hand modify the sequence of activation of neurons in real-time
• The intelligent activities like reasoning and comprehension results from logical activation of
neuron memory in right pattern and sequence giving rise to appropriate sensations
• The pattern and sequence depend on the pre-conditioning of synapses of the attention network
• The resultant sensations give rise to the feelings of will and enjoyment
• If the connections and synapses are optimized, right neurons are activated in right order leading
to better actions and better memory architecture
• Better memory architecture again leads to better attention control setting up a cycle of
interaction between memory and attention
• The logic which determines the time and sequence of activation of neurons of attention network
and subsequently activation of other neurons by attention network is intelligence

29. Unconscious,
subconscious and
conscious mind
• Unconscious
• Reticular formation is responsible for general state of arousal
• When the reticular formation does not allocate resources for memory
activation, there are no sensations
• Because of lack of sensations there is no consciousness
• Subconscious
• When there is automatic processing, the sensations are not remembered
• Series of sensations arise and extinguish, without activating the attention
mechanism.
• These unattended sensation constitute the subconscious mind
• Conscious
• Attention causes awareness of the sensations giving rise to the conscious
mind
• Attention controls sensory inputs giving more information about the object
of interest
• Attention can also ignore sensory inputs
• By ignoring unnecessary inputs and focussing on relevant sensations
attention causes more elaborate processing of information
• As a result, synapses are strengthened
• So, the information can be remembered
• This leads to awareness of the activity which is generally thought as
consciousness

30. Types of sensations and programming of
synapses (slide 1)
• When sensations represent the objects of the nature, then they are perceptual
• The sensations which are used to comprehend the perceptual sensations are conceptual
• Some sensation are qualitative
• They represent feelings like pain and pleasure
• The perceptual and conceptual sensations get associated with these qualitative feelings
• So different experiences produces different types of feelings like pain amd pleasure
• This becomes value to the perceptions and actions
• Some sensations become desirable and some actions become preferable
• Thus, presence of qualitive sensations creates a tendency for pursuit of pleasurable
activities and avoidance of painful activities

31. Types of sensations and programming of
synapses (slide 2)
• Neuromodulation by limbic system makes an individual to behave in a particular
way in a particular situation
• The autonomic system adjusts the body physiology to support those behaviours
• To work efficiently brain develops certain pre-sets which are subconsciously
activated by the triggering sensations and release appropriate neuromodulators
to adjust the excitability of neurons and synapses in the required way
• Emotions like anger and fear are such examples
• The neuromodulation affects both automatic and controlled processing
• The emotional and behavioural responses make an individual act in a predictable
and logical way
• The attention guided neural activities lead to memory consolidation and synaptic
strength modifications
• These changes are then utilized for automatic processing

32. Interaction between automatic and controlled
processing: Priming
• It has been observed that prior exposure to a stimulus can subconsciously
influence the response to another perceptually or conceptually related stimulus
• This is called priming
• Roediger, H. L. (1993). Implicit memory in normal subjects. Handbook of neuropsychology, 8,
63-131.
• For example, if a person is exposed to red color and the asked to name a fruit, the
likely response becomes a red fruit like apple
• When the priming stimulus is processed, the neurons responsible for processing
of related stimuli are also depolarized
• Depolarization increases the readiness for their activation
• If there is attention guided processing of a related stimuli, the depolarized
neurons get better chance to cross the threshold and generate action potential
• This explains the mechanism of priming memory

33. Sensations and the Concept of Self
• The stimulation of external sense receptors results in the concept of
the world
• This results in the experience that part of the world is under voluntary
control or direct source sensory feeling
• Thus, the reach of the nervous system divides the world into self and
non-self
• From the idea of self comes the idea of ‘I’, which is used for
understanding and communication

34. Types of personal memory
• Memory is divided into long- and short-term
• There are no separate memory stores for different types
• The division appears due to different mechanisms of activation of the schemata
• Long term memory
• ability of the neurons to produce sensations forms the basis of long-term memory
• A set of connected neurons contains a bit of information
• The information remains available as long as those neurons remain functional
• Implicit memory:
• Automatic processing of information results in activation of schemata as sensory memory
• If attention is not drawn, the sensations remain subconscious
• These subconscious activities appear as implicit memory
• Explicit memory
• Activation of schemata by controlled processing leads to awareness of the sensations
• Using the memory traces, learned facts or experienced episodes can be retrieved by generating required
pattern of activities

35. Working memory
• There is a limit to how much information can be attended at a time
• The limit appears to be about 7 characters (Miller, 1956)
• Unlike sensory memory, the sensation can last longer
• The sensations arising as a result of controlled processing constitute the working memory
• Baddeley Hitch model describes central executive, visuo-spatial sketch pad, phonological loop and episodic buffer
• It can be said that the executive functions are the result of a hierarchy in the network in terms of excitability
• The part of the network up in the hierarchy controls the activities in the lower order areas
• The understanding of the presence of a common library of schemata can easily explain the mechanisms of phonological loop and
visuo-spatial sketch pad
• Because of the prime-ability of the neurons, senses does not need to bring detailed information
• When a bit of information comes, the associated neurons which were activated in the past during a similar pattern of activity
• In familiar situations, a little information from the senses generate the understanding of what is happening now, what might have
happened in the past and what may happen in future
• Thus, priming of related neurons enables episodic buffer function
• Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological
review, 63(2), 81.

36. Basics of spatial processing (slide 1)
• There can be a dissociation between perception linked to awareness and perception linked to action
• Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in neurosciences, 15(1),
20-25.
• Parietal lobe
• It is responsible for egocentric movement
• However, it cannot identify the objects
• It can use visual cues and perform visually guided movements
• Perenin, M. T., & Vighetto, A. (1988). Optic ataxia: A specific disruption in visuomotor mechanisms: I. Different aspects of the deficit in
reaching for objects. Brain, 111(3), 643-674.
• Parietal lobe damage leads to conditions called spatial neglect and balint syndrome
• Hécaen, H., & De Ajuriaguerra, J. (1954). Balint's syndrome (psychic paralysis of visual fixation) and its minor forms. Brain, 77(3), 373-
400.
• Corbetta, M., & Shulman, G. L. (2011). Spatial neglect and attention networks. Annual review of neuroscience, 34, 569-599
• It can be concluded that parietal lobe creates a representation of space and awareness of objects in it
• Temporal lobe
• Temporal lobe is responsible for object recognition
• Karnath, H. O., Rüter, J., Mandler, A., & Himmelbach, M. (2009). The anatomy of object recognition—visual form agnosia caused by
medial occipitotemporal stroke. Journal of Neuroscience, 29(18), 5854-5862.

37. Basics of spatial processing (slide 2)
• entorhinal cortex contains grid cells, which fire at regular intervals as the animal moves
• Moser, E. I., Kropff, E., & Moser, M. B. (2008). Place cells, grid cells, and the brain's spatial representation system. Annual
review of neuroscience, 31(1), 69-89.
• These cells are also active when the extraocular muscles move the eyes
• Bicanski, A., & Burgess, N. (2019). A computational model of visual recognition memory via grid cells. Current Biology, 29(6),
979-990
• Entorhinal cortex receives processed inputs from sensory association areas and sends efferent to the
hippocampus
• Witter, M. P. (1993). Organization of the entorhinal-hippocampal system: a review of current anatomical data. Hippocampus
Vol. 3, Spl. Issue. Churchill Livingstone, New York, 33-44.
• The hippocampus contains neurons responsible for spatial perception
• O'Keefe, J., & Dostrovsky, J. (1971). The hippocampus as a spatial map: Preliminary evidence from unit activity in the freely-
moving rat. Brain research. 34, 171–175 (1971).
• Taube, J. S. (2007). The head direction signal: origins and sensory-motor integration. Annual review of neuroscience, 30(1),
181-207.
• Lever, C., Burton, S., Jeewajee, A., O'Keefe, J., & Burgess, N. (2009). Boundary vector cells in the subiculum of the
hippocampal formation. Journal of Neuroscience, 29(31), 9771-9777.
• Deshmukh, S. S., & Knierim, J. J. (2013). Influence of local objects on hippocampal representations: Landmark vectors and
memory. Hippocampus, 23(4), 253-267.

38. Basics of spatial processing (slide 3)
• Studies have shown that the HP and HD cell response are anchored to visual landmarks present in the environment (8, 9)
• O'Keefe, J., & Conway, D. H. (1978). Hippocampal place units in the freely moving rat: why they fire where they fire. Experimental brain research, 31(4), 573-590.
• Muller, R. U., & Kubie, J. L. (1987). The effects of changes in the environment on the spatial firing of hippocampal complex-spike cells. Journal of Neuroscience, 7(7), 1951-
1968.
• Place cells in the hippocampus are active when an individual navigates using vision, which continues to be active if the light is switched off, so long the
orientation persists
• Vestibular input has been seen to be important for activity of these cells (10)
• Stackman, R. W., & Taube, J. S. (1997). Firing properties of head direction cells in the rat anterior thalamic nucleus: dependence on vestibular input. Journal of
Neuroscience, 17(11), 4349-4358.
• The activity is present in blind animals as well where visual landmarks are absent (11)
• Save, E., Cressant, A., Thinus-Blanc, C., & Poucet, B. (1998). Spatial firing of hippocampal place cells in blind rats. Journal of Neuroscience, 18(5), 1818-1826.
• If movement of an animal is restrained, then the activity of these cells is attenuated (12)
• Foster, T. C., Castro, C. A., & McNaughton, B. L. (1989). Spatial selectivity of rat hippocampal neurons: dependence on preparedness for movement. Science, 244(4912),
1580-1582.
• Place cells in the hippocampus are active when an individual navigates using vision and if the landmarks are removed or light is switched off, then the
place cell activity continues for a while as long as the orientation of environment persists in memory
• Muller, R. U., & Kubie, J. L. (1987). The effects of changes in the environment on the spatial firing of hippocampal complex-spike cells. Journal of Neuroscience, 7(7), 1951-
1968.
• Quirk, Gregory J., Robert U. Muller, and John L. Kubie. "The firing of hippocampal place cells in the dark depends on the rat's recent experience." Journal of Neuroscience
10.6 (1990): 2008-2017.

39. Role of Hippocampus
• Lack of hippocampus cause loss of episodic memory
• By creating an allocentric spatial map of movement, it is able to process the context of an action
in terms of ‘where’ and ‘when’
• Preservation of the pattern of activity retains the allocentric spatial relationship and the sequence
of the patterns preserves the temporal information
• With its efferent connection it can contextually prime different cortical areas
• This contextual priming helps to understand and remember the context of present experience
• Preservation of activity pattern makes the episode rememberable
• Without hippocampus, contextual priming is lost and episodic information cannot be encoded
(antegrade amnesia) and past episodes cannot be remembered (retrograde amnesia)
• However if a specific contextual priming is repeated sufficient number of times the cortical
synapses become potentiated enough
• Then if a part of the sequence is activated the rest of the episode is directly primed
• Such episodes can be remembered without the help of hippocampus like semantic memory

40. Basic mechanisms of visual processing: retinal
ganglion cells to area V1
• A center surround antagonistic receptive field generates the basic information of visual processing, which was first observed in
retinal ganglion cells
• Kuffler, S. W. (1953). Discharge patterns and functional organization of mammalian retina. Journal of neurophysiology, 16(1), 37-68.
• The LGB neurons maintains similar center-surround receptive field organisation as the ganglion cells
• Hubel, D. H., & Wiesel, T. N. (1961). Integrative action in the cat's lateral geniculate body. The Journal of physiology, 155(2), 385-98.
• Convergence of neural connections into the V1 neurons, merges the receptive fields change, creating receptive fields with
demarcated areas
• V1 neurons are sensitive to the orientation of the edges of the receptive fields.
• Each neuron is sensitive to a particular direction and fire when the edge of a stimulus is oriented in that direction. called this
simple receptive field.
• Convergence of simple neurons takes place into neurons with complex receptive fields.
• The neurons processing the information from a particular area of the visual fields are clustered together and within a cluster, the
directions of response of the neurons change in a continuous manner
• Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. The Journal of
physiology, 160(1), 106-54.
• Hubel, D. H., & Wiesel, T. N. (1968). Receptive fields and functional architecture of monkey striate cortex. The Journal of physiology, 195(1),
215-243.

41. Basic mechanisms of visual processing: ocular
dominance columns
• At V1, initially the fibres do not mix with each other
• They remain segregated forming distinct stripes on the surface of V1.
These segregation leads to formation of ocular dominance columns74
• Adams, D. L., Sincich, L. C., & Horton, J. C. (2007). Complete pattern of ocular
dominance columns in human primary visual cortex. Journal of Neuroscience,
27(39), 10391-10403.
• The orientation columns converge upon these non-oriented cells
forming a swirl like arrangement
• Blasdel, G. G., & Salama, G. (1986). Voltage-sensitive dyes reveal a modular
organization in monkey striate cortex. Nature, 321(6070), 579-585.

42. Relationship between visual and spatial
perception
• A blind person can move around using other senses
• So, loss of vision does not abolish awareness of space
• Anomalies of spatial perception on the other hand affect visual perception
as seen in visual neglect and balint syndrome
• From these findings it can be concluded that, an intact spatial perception is
a prerequisite for visualisation of objects in space
• So brain must have a direct mechanism of spatial perception independent
of vision responsible for place cell activity in a blind animal
• Visualisation of objects in space is an indirect way of spatial perception
which causes the place cell activity during visually guided exploration

43. Direct spatial Perception
• The direct knowledge of position of an object in space and its spatial characteristics are obtained
through exploration of the environment
• Internal senses play important roles in it - the vestibular system maintains posture and balance
during movement and the proprioceptive sense sends feedback about movement of the body
parts
• When an object is encountered, its position and characteristics are known from this feedback
• The knowledge remains in the memory and is used for subsequent explorations
• More a terrain is explored, more information of its boundary and landmarks is stored in the
memory
• In this way an individual becomes aware of the spatial map of its environment
• The basic understandings of spatial features like distance, shape and size develop by direct
exploration, where visual senses play no primary role
• Without these concepts in the memory, it cannot be possible to identify objects and their position
in a visual representation
• That is why internal feedback of movement is the direct way of spatial perception

44. Relationship
between direct and
indirect space
perception

45. Importance of direct spatial perception
• An environment cannot be known through sense input only
• Exploration of the environment is essential
• Sensory inputs make one aware of the results of exploration
• The environment in known through movement in terms of magnitude and
direction
• For example distance tells how much movement is required to reach from one
place to another
• Similarly concept of shape comes from sense of direction
• Once these concepts are learned through movement, it becomes easy to figure
out the shape of the objects and the distance between then from sensory inputs
• Direct exploration also helps to develop conditioning between different modes of
perceptions like visual and spatial

46. Limitations of direct spatial perception
• For direct spatial perception, one has to thoroughly explore and remember
the spatial characteristics of an environment
• So, a lot of effort is needed to generate sufficient knowledge of the
environment
• Thus, the direct mechanism is time consuming and inefficient
• Without visual inputs, only a limited area of the environment can be
known
• Isolated visual sensations is of little use (Balint syndrome)
• But superimposed on intact spatial sensations, visual sensations create the
three-dimensional real-time view of the world, eliminating the need for
prior physical exploration of space

47. Classical conditioning:
Pavlov’s experiment
• McSweeney, F. K., & Bierley, C.
(1984). Recent developments in
classical conditioning. Journal of
Consumer Research, 11(2), 619-
631.
unconditioned
stimulus
Unconditioned
response
neutral stimulus
No conditioned
response
Conditioned
response
Conditioned
stimulus

48. Mechanism of visualisation of an object in
space: Indirect spatial perception
• Classical conditioning helps to explain how objects are visualised in space
• Based on retinal photoreceptors input, a visual representation is created
• The visual representation alone must be two dimensional
• Because of past experience of movement and viewing simultaneously, a conditioning develops
• This conditioning excites appropriate spatial memory based on the edges detected in the visual
representation
• As a result spatial awareness develops instantly which otherwise would take extensive physical
effort and time
• This process identifies objects in the visual representation and projects them into three
dimensional space, so that everything fits into a perspective
• This projection is imaginary like a dream experience
• Because it is based on both receptor stimulation and memory of past movement, when
movement is made according to the projection, the object is encountered at the predicted place
• Thus it is an indirect way of perceiving spatial objects

49. Limitations of indirect spatial perception
• Visual system provides many monocular cues for spatial perception
• They are sufficient for navigation of space but they are not enough for precise actions at closed
range
• This becomes evident when an object is reached one eye closed
• The judgement of depth is more accurate when both eyes are used instead of one eye
• This is because use of two eyes together requires use of eye muscles
• Feedback from these muscles generate direct spatial cues from the proprioceptive receptors of
eye muscle
• So visually guided movement uses three sensory inputs
• Direct proprioceptive feedback from the body muscles
• Indirect spatial perception from Visual sensation
• Binocular direct spatial cues coming from the eye muscles
• The anatomical configuration of visual pathway including the chiasma and the ocular dominance
columns play important roles in generation of Binocular direct spatial cues

50. Binocular vision and integration of visual and
proprioceptive inputs
• Ocular movements generate depth cues with the help of the internal and the external ocular muscles.
• Grid cells in entorhinal cortex must be playing a role in the recognition process by quantifying the proprioceptive inputs from the ocular muscles,
internal and external
• Though each eye can generate monocular depth cues, the accuracy of ocular spatial cues is greatly enhanced by the binocular vision
• Because of the crossing over of the nasal fibers at chiasma, each hemisphere of the brain receives the input from the contralateral visual fields of both
eyes
• The information reaches primary visual cortex side by side
• This gives rise to the ocular dominance columns
• It is like images from two projectors are being projected in the same screen at the same tome
• As two eyes remain horizontally apart their images differ from each other
• When the information from ocular dominance columns converge into next set of neurons the dissimilarity leads to physiological diplopia
• By converging the eyes on the point of fixation the diplopia disappear around the point of fixation
• Crossed diplopia develops for all proximal objects and uncrossed diplopia develops for all distal object
• Next the internal muscles must adjust the refractive power to bring the object into focus and the external muscles maintain the fixation
• Muscle activities generate direct spatial cues for determination of position and spatial features of the objects
• The physiological diplopia creates a sense of depth and the spatial cues from the ocular muscles increase accuracy of body movement

51. Limitations of visuo-spatial perception
• Visuo-spatial perception creates an appearance of a three dimensional
world all around
• It is often not remembered that this view is a representation of the ‘real
thing’ and not the ‘thing in itself’
• It is a collection of sensations produced by orderly neural stimulation
• With the help of the representation, accurate movements can be made
within the limits of natural human abilities
• However the view is relative
• Inaccuracies between expectation and actual observation of a movement
become evident when the limits are stretched a little further necessitating
the theory of relativity

52. Thus this work explains
• Neural basis of memory
• Neural basis of consciousness
• Neural basis of intelligence
• Neural basis of perception
• Neural basis of visualisation in three dimensional space